Implicit Differentiation

Show that the set defined by the equations
[tex]x + y + z + w = sin(xyzw)[/tex]

[tex]
x - y + z + w^2 = cos(xyzw) - 1[/tex]
can be described explicitly by equation of the form (z, w) = f(x, y) near the point (0,0,0,0); find the first partial derivatives of f(x,y) at the point (0,0)